Express your answer as a mixed number simplified to lowest terms. $15\dfrac{6}{7}-9\dfrac{4}{7} = {?}$
Explanation: Separate the whole numbers from the fractional parts: $= {15} + {\dfrac{6}{7}} - {9} - {\dfrac{4}{7}}$ Bring the whole numbers together and the fractions together: $= {15} - {9} + {\dfrac{6}{7}} - {\dfrac{4}{7}}$ Subtract the whole numbers: $=6 + {\dfrac{6}{7}} - {\dfrac{4}{7}}$ Subtract the fractions: $= 6+\dfrac{2}{7}$ Combine the whole and fractional parts into a mixed number: $= 6\dfrac{2}{7}$